The invention relates to a composite shock absorber for a PDC (polycrystalline diamond compact) bit. The composite shock absorber comprises a drilling tool body, an impact body, a disc spring set, a torsion bar spring and an annular pressing sleeve, wherein the bit vibration impact force is transmitted between the drilling tool body and the impact body through a torsion transmission joint, the impact body is arranged at the lower end of the drilling tool body and forms a shock absorption cavity, the drilling tool body is provided with a water inlet, the impact body is provided with a water outlet, the torsion bar spring is a cylindrical body, the upper end of the torsion bar spring is provided with an external thread, the lower part of the torsion bar spring is provided with a spline, thetorsion bar spring is positioned in the shock absorption cavity, the upper end of the torsion bar spring is connected to the drilling tool body in a threaded mode, the lower part of the torsion bar spring extends into an impactor and is connected to the impactor through the spline, the disc spring set sleeves the outer side of the torsion bar spring, the annular pressing sleeve is arranged at thelower end of the disc spring set, and a bearing set is arranged between the lower end surface of the annular pressing sleeve and an annular step, located in the drilling tool body, of the impact body.According to the composite shock absorber, the damage of the slippage effect to PDC cutting teeth can be weakened, the axial vibration from a drill string can be absorbed, and the service life of thebit can be effectively prolonged.